Factors controlling soil carbon and nitrogen stores in pure stands of Norway spruce ( Picea abies) and mixed species stands in Austria

Abstract

Soil data of 18 pairs of secondary pure spruce stands ( Picea abies) and adjacent mixed stands of spruce and broadleaf trees (at least 40% broadleaf trees, mainly beech, Fagus sylvatica) on comparable sites were used to study effects of species composition and other driving forces on carbon and nitrogen stores. It was hypothesized that carbon input by litter and roots to different soil horizons has a marked effect on carbon and nitrogen stores and, therefore, silvicultural methods, e.g., admixture of beech versus spruce, can be used to manage nitrogen retention and release. The study sites of different stand age (pole to mature stage) were chosen on two different bedrock materials (Flysch and Molasse). In general, soils on Flysch are less acidic, better supplied with nutrients, and less sandy than soils developed on Molasse. Species composition did not affect total stores (forest floor and 0–50 cm mineral soil) of carbon or nitrogen on Molasse, however, paired samples tests indicated that mean total stores were significantly higher both for carbon and nitrogen for pure spruce stands than for mixed species stands on Flysch. Carbon stores of the whole soil profile were best predicted by admixture of spruce, stores of phosphorus, sodium and calcium as well as stand age on Flysch; on Molasse, the only given predictor was aluminum storage, indicating that acidic soil conditions favor accumulation of organic carbon. On Flysch, total nitrogen stores were best explained by stores of sulfur and of the sum of base cations.